Lk 24:19, 25-26, Lk 24:32, 44-45, Jn 12:16
Before the disciples believed Jesus was the Christ, they knew Jesus as a mighty prophet. At that time, the Old Testament and the words of Jesus were not understood. (Lk 24:19, 25-26, Jn 2:22)
Lk 24:19 And he said unto them, What things? And they said unto him, Concerning Jesus of Nazareth, which was a prophet mighty in deed and word before God and all the people: 25 Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken: 26 Ought not Christ to have suffered these things, and to enter into his glory?
Jn 2:22 When therefore he was risen from the dead, his disciples remembered that he had said this unto them; and they believed the scripture, and the word which Jesus had said.
When the disciples saw the resurrected Jesus and truly believed that Jesus was the Christ, the Old Testament and the words of Jesus were understood. (Lk 24:32, 44-45, Jn 12:16)
Lk 24:32 And they said one to another, Did not our heart burn within us, while he talked with us by the way, and while he opened to us the scriptures? 44 And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. 45 Then opened he their understanding, that they might understand the scriptures,
Jn 12:16 These things understood not his disciples at the first: but when Jesus was glorified, then remembered they that these things were written of him, and that they had done these things unto him.